Arrangement for pumping a filtered fluid

ABSTRACT

A feed pump supplies a fluid through a filter to a main pump which pumps the fluid in filtered condition to a consumer. When the filter becomes clogged, a valve responsive to the increased pressure differential upstream and downstream of the clogged filter, supplies fluid for operating either a control valve connecting the outlet and inlet of the main pump and causing idle circulation of the fluid, or a hydraulic regulating means for setting the main pump to a minimum discharge.

United States Patent [1 1 Zellbeck et al.

[ Dec. 11, 1973 ARRANGEMENT FOR PUMPING A FILTERED FLUID [75] Inventors:Gustav Zellbeck,

Esslingen-l-legensberg; Paul Bosch, Ludwigsburg; Karl Veil, Uhingen;Gerhard Lutz, Faurndau, all of Germany [73] Assignee: Robert BoschGmhll, Stuttgart,

Germany [22] Filed: May 20, 1971 [21] Appl. No.: 145,301

[30] Foreign Application Priority Data May 21, 1970 Germany P 20 24675.7

[52] U.S. Cl. 210/130, 210/416 [51] Int. Cl ..B01d 29/36, B0ld 35/14[58] Field of Search 210/130, 133, 97,

[56] References Cited UNITED STATES PATENTS 2,865,442 12/1958 l-lalfordet a1 210/130 X Rosaen 210/130 3,618,777 11/1971 Meyer 210/130 3,013,57412/1961 Breting et al. 210/130 X 2,868,382 1/1959 Best 210/130 X PrimaryExaminer-John Adee Attorney-Michael S. Striker [57] ABSTRACT A feed pumpsupplies a fluid through a filter to a main pump which pumps the fluidin filtered condition to a consumer. When the filter becomes clogged, avalve responsive to the increased pressure differential upstream anddownstream of the clogged filter, supplies fluid for operating either acontrol valve connecting the outlet and inlet of the main pump andcausing idle circulation of the fluid, or a hydraulic regulating meansfor setting the main pump to a minimum discharge.

18 Claims, 4 Drawing Figures PATENTEDUEE 11 mm 3.777.888

saw 1 or 2 NE N 7 0 RS 4 Gus/9v zezwscx Paul B 056/1 Karl VE/I. GerhardL (/72 BY a My, ATTORNEY ARRANGEMENT FOR PUMPING A FILTERED FLUIDBACKGROUND OF THE INVENTION Apparatus is known for filtering a fluidsupplied by a feed pump through a filter to a main pump connected with aconsumer conduit. In accordance with the prior art, a bypass valve isprovided which, when the filter is clogged, or the fluid is a viscousliquid, particularly in cold condition, directs unfiltered fluid to themain pump. When unfiltered fluid is pumped by the main pump,particularly a piston pump, great wear occurs, and frequently the mainpump fails.

SUMMARY OF THE INVENTION It is the main object of theinvention toprovide an arrangement in which only filtered fluid can be pumped by amain pump to a consumer.

Another object of the invention is to prevent operation of the main pumpwhen the filter-is in a faulty condition.

Another object of the invention is to use a high pressure differentialoccurring in a faulty condition of the filter, for operating controlmeans which prevent the operation of the main pump with unfilteredfluid.

Another object of the invention is to provide pressure operated controlmeans which control the flow of fluid through the filter to the mainpump depending on the pressure differential occurring at the filter.

In this manner, an unfiltered flow of fluid from the feed pump to themain pump is prevented, so that the span of life of the main pump issubstantially increased. The arrangement of the invention is operativewhen the filter is clogged by dirt filtered out of the fluid passingthrough the filter, and also when the fluid is a viscous liquid, as mayoccur when the pumps are started in cold condition of the fluid, or bothfaulty conditions may simultaneously occur.

An embodiment of the invention comprises a main pump and a consumerconduit through which the main pump discharges a fluid supplied by afeed pump through a feed conduit means including a filter having aworking condition causing a normal pressure differential in the feedconduit; pressure responsive means, preferably including a pressureresponsive valve, connected with the feed conduit upstream anddownstream of the filter, and being in a normal inoperative positionwhen the normal pressure differential indicates the working condition ofthe filter; and control means for the main pump means.

The pressure responsive means moves to an actuating position in responseto a predetermined pressure differential different from the normalpressure differential, and indicating a faulty filtering action of thefilter. The control means terminate discharge through the comsumerconduit by the main pump when the fluid supplied by the pressureresponsive means in the actuated position operates the control means.

In one embodiment of the invention, the main pump pumps a constantamount of fluid, and discharge into the consumer conduit is prevented bya control valve causing idle circulation of the fluid pumped by the mainpump.

In another embodiment of the invention, regulating means are providedfor the main pump, and are operated by fluid by the pressure responsivemeans to reduce the output volume of fluid of the main pump when a highpressure differential at the filter indicates a faulty condition of thesame.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic and diagrammaticview illustrating a first embodiment of the invention;

FIG. 2 is a schematic and diagrammatic fragmentary view illustrating asecond embodiment of the invention in which the output of the main pumpis regulated;

FIG. 3 is a schematic and diagrammatic view illustrating a thirdembodiment of the invention; and

FIG. 4 is a schematic and diagrammatic view illustrating a fourthembodiment of the invention in which the output of the main pump isautomatically regulated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment 11 shown in FIG.1 has a feed pump 12 which pumps a fluid through a feed conduit havingan upstream portion 13 and a downstream portion 15 between which afilter 14 is located, so that the fluid supplied by feed pump 12 throughthe feed conduit 13,15 and filter 14 to the inlet of a main pump 16 iscontinuously filtered. Main pump 16 is driven, together with feed pump12 by a prime mover, not shown, and pumps the fluid into a consumerconduit 170,17 connected with consumer apparatus 18, such as hydraulicmotors. A control valve 37 is provided between the conduit portions 17aand 17 of the consumer conduit.

A first discharge conduit 19 branches off the feed conduit portion 13upstream of filter 14, and discharges into a reservoir 21 which may beconnected with the inlet of feed pump 12. A schematically illus tratedpressure responsive valve 22, located in the discharge conduit 19,includes a schematically shown valve member 24 shiftable between anormal inoperative position and an actuated position. A spring 23abutting the valve casing, biasses valve member 24 to a normalinoperative position 25 in which discharge conduit 19 is closed, and inwhich a first control conduit 26 is separated from the conduit 19 andfeed conduit portion 13. Valve 22 is constructed similar to valve 97shown in FIG. 4.

A control channel 19" connects conduit 19 and the feed conduit portion13 upstream of filter 14 with one end of the casing of valve 22 to exerta pressure opposing the pressure of spring 23 on valve member 24.Another channel 19' connects a discharge conduit 28, and the feedconduit portion 15 downstream of filter 14 with the other end of thecasing of pressure responsive valve 22 so that the pressure in channel19' is added to the force of spring 23 and urges the valve member 24into the normal inoperative position.

When the filter is in good working condition, and its flow resistance islow, the pressure differential between channels 19' and 19" is small,and insufficient for overcoming the force of spring 23 so that all thefluid pumped by feed pump 12 passes through the filter 14 to the mainpump 16. However, when the filter is clogged, and its flow resistance ishigh, the pressure differential is increased, and the force exerted bythe pressure fluid in channel 19" is sufficient to move valve member 24to a second actuated position schematically indicated at 27, in whichthe fluid pumped by feed pump 12 into feed conduit portion 13 isdischarged through discharge conduit 19 into the reservoir 21, and alsothrough a first control conduit 26 to flow to a control valve 37 locatedin the consumer conduit between consumer conduit portions 17a and 17.

The seconddischarge conduit 28 branches off the feed conduit portion andhas a discharge outlet opening into reservoir 21. A pressure limitingvalve 29 is provided in discharge conduit 28, and includes a movablevalve member 32 urged by a spring 31 to a first position 33 closingdischarge conduit 28, and also a second control conduit 34 which isconnected to the control valve 37. The casing of pressure limiting valve29 is connected at one end with channel 19' which is connected to thedownstream portion 15 of the feed conduit, and acts on the valve member32 of the pressure limiting valve 29 in -a direction opposite to theforce of spring 31. When the pressure is sufficiently high in channel19' due a good condition of filter 14, the spring force of spring 31 isovercome, and valve member 32 moves to a second position 35 in whichfluid from feed conduit portion 15 is supplied through discharge conduit28 and a duct in valve member 32 to the second control conduit 34. Ifthe pressure further increases, the valve member 32 moves to a thirdposition 36 in which the second control conduit 34 is connected with thefeed conduit portion 15, as before, but in which the discharge conduit28 is connected with the discharge outlet into reservoir 21 so that thepressure in the second control conduit 2 cannot become excessively high.

The control valve 37 between the consumer conduit portions 17a and 17,has a movable valve member 39 urged by spring 38 to a control position41 in which consumer conduit portion 17a is connected with a return orbypass conduit 42 which is connected to feed conduit portion 15downstream of filter 14 and thereby with the inlet of main pump 16 sothat in the position of the control valve 37 shown in FIG. 1, the mainpump 16 idly circulates the fluid supplied by the feed pump 12, and nofluid flows through the consumer conduit portion 17 to the consumerapparatus 18.

The first control conduit 26 has a port in valve casing of valve 37 sothat the fluid pressure in control conduit 26 acts on valve member 39 tomove to the illustrated control position 41. The second conduit 34 isconnected to the other end of the casing of control valve 37 and urgesvalve member 39 in the direction opposite to the force of spring 38 toan inoperative position in which the consumer conduit portions 17a and17 are directly connected, and the main pump 16 discharges fluid throughconsumer conduit 12,17 to consumer apparatus 18.

The embodiment of FIG. 1 operates as follows.

The feed pump 12 supplies fluid through filter 14 and the feed conduit13,15 to the inlet of the main pump 16 whose output discharges aconstant volume of fluid. The output volume of feed pump 12 is alwaysslightly greater than the absorption volume of the main pump 16, so thata certain filling pressure prevails in the feed conduit portion 15determined by the pressure limiting valve 29. This filling pressure hasthe effect that valve member 32 is operated to assume at least theposition 35 in which pressure fluid is supplied from feed conduitportion 15 through control conduit 34 to the control valve 37. Since nofluid is supplied through control conduit 26 to control valve 37, thepressure created by control conduit 34 causes movement of control valvemember 39 to the position 43 in which the duct in valve member 39connects the consumer conduit portions 17a and 17 so that the main pump16 supplies fluid to the consumer apparatus 18 as long as the fillingpressure in feed conduit portion 15 is sufficiently high to operate thepressure limiting valve 29.

If a required filling pressure is not reached in feed conduit portion15, or drops, the spring 31 urges valve member 32 to position 33 inwhich no fluid is supplied to control conduit 34'so that spring 38 movescontrol valve member 39 of control valve 37 to the control positionshown in FIG. 1 in which the fluid is idly circulated by main pump 16through return conduit 42.

A pressure differential occurs upstream and downstream of filter 14which acts by fluid in channels 19 and 19" on valve member 24 of thepressure responsive valve 22 against the force of spring 23. The forceof spring 23 is adjusted to a predetermined pressure corresponding tothe permissible pressure differential at filter 14. As long as filter 14is not very dirty, the pressure drop at filter 14 is at the permissiblepressure differential, and the valve member 24 of pressure responsivevalve 22 remains in the normal inoperative position 25.

In the event that dirt deposited in filter 14 increases the flowresistance of filter 14, the pressure drop at filter 14 causes apressure differential which is sufficient to overcome the force ofspring 23 so that valve member 24 moves to the actuated position 27 inwhich ducts in valve member 24 connect feed conduit portion 13 with thedischarge reservoir 21, and also with the control conduit 26 so that inthe same pressure fluid from feed pump 12 flows to control valve 37,acting on control valve member 39 to move the same to the illustratedposition in which the fluid pumped by main pump 16 idly circulates inreturn conduit 42. The control valve 37 is constructed as a three-wayvalve so that, except of leakage flow through control valve 37, no fluidis pumped through consumer conduit portion 17 to consumer apparatus 18.In an extreme case, only so much fluid needs to flow through filter 14that the leakage losses of the main pump 16 are covered.

An increased pressure differential, with the consequent termination ofdischarge from main pump 16 through consumer conduit portion 17, mayalso be due to a cold condition of a viscous liquid pumped through feedconduit 13,15 by feed pump 12. In this event, the flow of the liquidthrough the ducts of valve member 24 in the position 27 has a throttlingeffect by which the fluid is heated, so that the apparatus becomesoperative. Shifting of valve member 24 of pressure responsive valve 22while the pumped fluid is in sufficiently warm condition, is anindication that the filter operation is faulty, and that the filter 14must be exchanged.

The embodiment ll of FIG. 1 assures that only the filtered fluid entersthe main pump 16. Since pressure responsive valve 22 is controlled bythe pressure differential at filter 14, filter 14 is protected from anexcessively high pressure differential. The filling pressure set by thepressure limiting valve 29, can be selected independently of thepressure differential required for shifting pressure responsive valve22. As long as the filling pressure is not reached, it is not possibleto operate the main pump 16 to pump at full pressure.

The embodiment of FIG. 2 is identical with the embodiment of FIG. 1 asfar as the elements on the left side of the chain line I-I'areconcerned, but FIG. 2 illustrates a modification of the parts shown onthe right side of the line II. The first control conduit 26, the secondcontrol conduit 34, and the feed conduit portion are shown to cross theline I--l.

The embodiment 50 shown in FIG. 2 has a variable output main pump 51controlled by regulating means 52. The output of main pump 51 dischargesthrough consumer conduit 17' to consumer apparatus 18. The output ofmain pump 51 can be varied manually by the manual linkage 53 which hasan arresting recess schematically shown at 54 cooperating with anarresting member 55 operated by a piston and cylinder means 56. Thechamber 58 on one side of the piston is connected with control conduit26, which also extends to the regulating means 52, and chamber 57,through which the piston rod passes to arrestingmember 55, is connectedwith the second control conduit 34. A spring 55a acts on arrestingmember 55 in the same direction as fluid in chamber 58.

The embodiment of FIG. 2 operates as described with regard to theembodiment of FIG. 1, as far as the parts on the left side of the lineI-I are concerned. When the pressure responsive valve 22 moves to anactuated position due to the high pressure differential at the filter14, valve member 24 assumes the position 27 so that the feed pump 12pumps pressure fluid through feed conduit portion 13, conduitl9,valve'member 24 into the first control conduit 26so that the fluid inthe regulating means 52 operates the same to set main pump 51 to minimumoutput flow. Manual means 53 are operated, and due to the pressure fromcontrol conduit 26 in chamber 58, arresting member 55 moves intoarresting recess 54 and locks the regulating means of main pump 51 inthe position of minimum output flow. When the required filling pressureis again obtained in feed conduit portion 15, pressure limiting valve 29responds so that in the position 35 of pressure limiting valve 29,pressure fluid flow through the second'control conduit 34 into chamber56 so that arresting member 55 is withdrawn.

When the output of main pump 51 is reduced to a minimum, no unfilteredfluid is supplied to the consumer apparatus. At the same time, fluidpumped by feed pump 12 into discharge conduit 19, is discharged into thereservoir 21, so that the amount of fluid fiowing through filter l4 issubstantially reduced.

The third embodiment 60 shown in FIG. 3 has a feed pump 61 which pumpsfluid through a feed conduit portion 62, a filter 63, and another feedconduit portion 64, into the main pump 65 which is a constant outputpump discharging into a consumer conduit 66 fluid toward consumerapparatus 67. The feed conduit portion 62 upstream of filter 63 isconnected by a pressure limiting valve 68 to a discharge outlet openinginto a reservoir 69 from which feed pump 61 pumps fluid. The pressurelimiting valve 68 has a normal closed position, and is held in the sameby a spring 68a.

Consumer conduit 66 is connected by a bypass conduit 71 with a pressureresponsive control valve 72 which has a casing with ports for the bypassconduit 71, and other ports for control conduits 62',62" which areconnected with feed conduit 62,64 downstream and upstream of filter 63,respectively, so that the pressure differential of filter 63 acts on thevalve member 74, schematically shown, in addition to the spring 73. Inthe illustrated position, no fluid can flow through bypass conduit 71into the feed conduit portion 64, but when valve 72 is shifted by anincreased pressure differential caused by faulty condition of filter 63,a duct, schematically shown as an arrow, connects the interruptedportions of bypass conduit 71 so that the fluid pumped by main pumpflows through conduits 71 and 64 from the outlet of the main pump 65 toan inlet. A check valve is provided in the feed conduit portion 64downstream of the bypass conduit 71.

The operation of the embodiment 60 shown in FIG. 3 correspondssubstantially to the operation of the embodiment of FIG. 1, and thepressure differential occurring at the filter 63 is used for controllingthe fluid flowing through filter 63 to the constant output pump 65.Control valve 72 shunts pump 65 when the permissible pressuredifferential at filter 63 is exceeded, and the pressure responsivecontrol valve 72 responds and shifts valve member 74 to the position inwhich main pump 65 is shunted by conduit 71,64.

The pressure limiting valve 68 determines the filling pressure for themain pump 65. In order to prevent damage to filter 63, the pressuredifferential to which pressure responsive control valve 72 responds, isselected in accordance with the permissible pressure drop at filter 63.Check valve 75 prevents that pressure surges from consumer apparatus 18'reach and affect filter 63. Thefunction of the arrangement is assured,as long as, at the greatest permissible pressure differential, theamount. of fluid flowing through filter 63 is greater than the leakagedischarge of the main pump 65.

In the embodiment shown in FIG. 4, a feed pump 81 pumps through a feedconduit portion 82, a filter 83, and a second feed conduit portion 84,fluid to the main pump 85 which discharges fluid through a consumerconduit 86 to consumer apparatus 87. A pressure limiting valve 88 has adischarge outlet 89 into a reservoir 103 from which feed pump 81 andmain pump 85 may suck fluid. Pumps 81 and 85 are connected for rotationand driven by prime mover, not shown.

The main pump 85 is provided with regulating means by which the amountof fluid discharged through the outlet can be regulated under thecontrol of a cylinder and piston motor 90. The differential piston 92divides the cylinder into a piston rod chamber 93 and a piston chamber94. A manually operated member 91 is connected with piston 92 and can bemanually placed in a position in which the volume of chamber 93 is aminimum. Chamber 93 is connected by a conduit 95 with consumer conduit86 and with the outlet of main pump 85, while chamber 94 is connected byconduit 96 with a pressure responsive valve 97 whose casing ends areconnected by channels 101 and with the feed conduit portions 82 and 84upstream and downstream of filter 83, respectively. A spring 98 in thevalve casing urges valve member 99 in the same direction as the pressurefluid of channel 100. Valve member 99 of the pressure responsive valve97 has a normal position in whichthe conduit 96, and thereby chamber 94,is disconnected from a discharge conduit 102 which opens into areservoir 103. In the actuated position of valve member 99, conduit 96is connected with discharge conduit 102, so that fluid is dischargedfrom cylinder chamber 94.

The operation of the embodiment 80 shown in FIG. 4 correspondssubstantially to the operation of the embodiment 50 of FIG. 2, since thepressure drop at filter 83 is used for adjusting the regulating means 90of the variable main pump 85.

As long as the pressure drop at filter 83 does not exeed a certainpermissible value, feed pump 81 pumps fluid through filter 83 and feedconduit 82,84 into the inlet of main pump 85 which discharges into theconsumer conduit 86. Pressure limiting valve 88 determines the fillingpressure in feed conduit portion 82. The pressure in consumer conduit 86acts also through conduit 95 in chamber 93, while chamber 94 and conduit96 are separated from discharge outlet conduit 102 by pressureresponsive valve 97.

Main pump 85 can be regulated by the regulating means 90, and when themanual member 91 moves piston 92 to a position reducing chamber 93 to aminimum by moving the piston rod as far out of the cylinder as possible,main pump 85 operates at the maximum output flow. If in this conditionof main pump 85 and the regulating means 90, the pressure drop at filter83 reaches a predetermined value due to high viscosity of the fluid, ordue to clogging of filter 83, the pressure responsive valve 97 respondsand valve member 99 is shifted, connects conduit 96 with conduit 102,and relieves chamber 94 of the regulating means 90 so that fluid flowsout of chamber 94, and is discharged through conduit 96 and 102.

Fluid flowing through conduit 95 into chamber 93 acts on differentialpiston 92 so that main pump 85 is adjusted and set to a smaller outputflow. The amount of fluid flowing through filter 83 is correspondinglyreduced, since main pump 85 is mechanically coupled with feed pump 85for rotation. The excess fluid pumped by feed pump 81 flows through thepressure limiting valve 88 into the discharge conduit 89 which opensinto reservoir 103.

When the pressure drops at filter 83 is again reduced to the permissiblevalue, pressure responsive valve 97 interrupts the connection betweenconduits 96 and 102 so that the normal operation can take place.

In the embodiment 80 of FIG. 4, the main pump 85 can be regulated onlyin a negative direction from maximim output to a zero position at aminimum output. The arrangement could be modified by providing aregulation in the positive direction, which would require instead of thereturn discharge conduit 102 to reservoir 103, a conduit connecting thepressure responsive valve 97 with the consumer conduit 86. In such anarrangement, the differential piston 92 would effect a return from apositive range of adjustments.

The hydraulic servo motors 56,90 shown for controlling the regulatingmeans of the main pump in the embodiments of FIGS. 2 and 4 could bereplaced by other regulating means, in which, for example, spring meansare provided for returning the servo motor to a neutral position.

High pressure or low pressure may be used for the operation of thehydraulic regulating means for the variable main pumps, and the pressurefluid may come from a consumer system, or from an independent source ofpressure fluid. The embodiments of FIGS. 1 and 3 in which main pumps ofconstant output volume are used, can be modified so that the main pumpsare partly or completely shunted.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofarrangements for pumping filtered fluid differing from the typesdescribed above.

While the invention has been illustrated and described as embodied in anarrangement having pressure responsive control means responding to anexcessive pressure drop at a filter for controlling the flow of a fluidfrom a feed pump through the filter to a main pump supplying consumerapparatus, it is not intended to be limited to the details shown, sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

We claim:

1. Arrangement for pumping a filtered fluid, comprising a feed pump;main pump means including a main pump, and a consumer conduit throughwhich said main pump discharges;

feed conduit means connecting said feed pump with said main pump so thatonly fluid pumped by said feed pump into said feed conduit means flowsinto said main pump;

filter means in said feed conduit means having a working conditioncausing a normal pressure differential in said feed conduit means, saidfilter means being disposed across the flow cross section of said feedconduit means so that all the fluid flowing in said feed conduit meansto said main pump means flows through said filter means, and no fluid inunfiltered condition bypasses said filter means and flows into said mainpump;

pressure responsive means connected with said feed conduit meansupstream and downstream of said filter means and being in a normalinoperative position when said normal pressure differential indicatessaid working condition of said filter means, said pressure responsivemeans moving to an actuated position in response to a predeterminedpressure differential different from said normal pressure differentialand indicating a faulty filtering action of said filter means;

and control means for said main pump means operated by said pressureresponsive means in said actuated position to terminate discharge fromsaid main pump into said consumer conduit.

2. Arrangement as claimed in claim I wherein said main pump discharges aconstant amount of fluid; wherein said control means include a controlvalve means having an operative position connecting said main pump withsaid consumer conduit, and a control position in which said main pumpidles; and wherein said pressure responsive means include a pressureresponsive valve responding to said predetermined pressure differentialto move to said actuated position, and connecting in said actuatedposition said feed conduit between said feed pump and said filter meanswith said control valve means for moving the same from said normalposition to said control position.

3. Arrangement as claimed in claim 1, wherein said control means includehydraulic regulating means for said main pump; and wherein said ressureresponsive means include a pressure responsive valve. responding to saidpredetermined pressure differential to move to said actuated position,and connecting in said actuated position said feed conduit between saidfeed pump and said filter means with said hydraulic regulatingmeans sothat fluid flowing from said feed pump to said hydraulic regulatingmeans operates the latter to set said main pump to pump a minimum amountof fluid.

4. Arrangement as claimed in claim 1 wherein said pressure responsivemeans include a pressure responsive valve including a movable valvemember, and a spring biassing said valve member into said normalinoperative position; wherein said control means include a controlconduit; wherein said valve in said actuated position connects said feedconduit and said control conduit, respectively; wherein saidpredetermined pressure differential overcomes the force of said springand moves said valve member to said actuated position; and wherein saidcontrol means are hydraulic control means operated in said actuatedpositionof said valve by fluid flowing from said feed pump through saidvalve and said control conduit.

5. Arrangement as claimed in claim 1 comprising a discharge conduitconnected with said feed conduit downstream of said filter means; and apressure limiting valve in said discharge conduit spring biassed to afirst position closing said discharge conduit when the pressure in saidfeed conduit is low, and at least a second position for supplying fluidto said control means for holding the same in a normal position in whichsaid main pump discharges through said consumer conduit fluid fed bysaid feed pump at a normal pressure.

6. Arrangement as claimed in claim 1 wherein said control means includea control valve means including a control valve member, a valve casing,and a spring biassing said control valve member to a first positionclosing said consumer conduit; comprising a return conduit connectingsaid valve casing with said feed conduit downstream of said filter meansand being connected with said consumer conduit in said first position sothat said main pump idles, said control valve member having a secondworking position closing said return conduit and opening said consumerconduit; first and second control conduits connected with ,said valvecasing so that pressure in said first control conduit acts on saidcontrol valve member to move the same to said first position, andpressure in said second conduit acts on said control valve member tomove to said second working position; wherein said pressure responsivemeans include a pressure responsive valve connecting in said actuatedposition said feed conduit between said feed pump and said filter meanswith said first control conduit so that at said predetermined pressuredifferential said control valve member closes said consumer conduit; andcomprising a pressure limiting valve connected with said feed conduitdownstream of said filter means and including a limit spring urging saidpressure limiting valve to a closed position, said pressure limitingvalve moving to an operative position connecting said feed conduit withsaid second control conduit when the pressure in said feed conduitovercomes the force of said limit spring so that said control valvemember is moved to said second working position.

7. Arrangement as claimed in claim 6 wherein said pressure limitingvalve in said closed and operative positions disconnects said feedconduit from a discharge outlet, and has a third position assumed athigh pressure in said feed conduit for connecting said feed conduit withsaid discharge outlet and with said second control conduit.

8. Arrangement as claimed in claim 1 wherein said control means includehydraulic regulating means for said main pump; wherein said pressureresponsive means include a pressure responsive valve responding to saidpredetermined pressure differential to move to said actuated position,and connecting in said actuated position said feed conduit between saidfeed pump and said filter means with said hydraulic regulating means sothat fluid flowing from said feed pump to said hydraulic regulatingmeans operates the latter to set said main pump to pump a minimum amountof fluid; and wherein said regulating means further include manuallyoperated means, and hydraulic arresting means for arresting saidmanually operated means.

9. Arrangement as claimed in claim 8 comprising a pressure limitingvalve connected with said feed conduit; wherein said hydraulic arrestingmeans include a cylinder, and a piston forming in said cylinder firstand second chambers; said first chamber being connected by said pressureresponsive valve with said feed conduit upstream of said filter means,and said second chamber being connected by said pressure limiting valvewith said feed conduit downstream of said filter means; and wherein saidhydraulic arresting means further include an arresting member operatedby said piston so that said manually operated means are arrested whenhigh pressure fluid from said feed conduit is supplied to said firstchamber, and are released by high pressure fluid supplied to said secondchamber.

10. Arrangement as claimed in claim 1 wherein said pressure responsivemeans include a valve casing, two conduits connecting said valve casuingwith said feed conduit upstream and downstream of said filter means, avalve member in said casing between said conduits so that the pressuredifferential caused by said filter means acts on said valve member, anda spring acting on said valve member and urging the same into saidnormal inoperative position, said predetermined pressure differentialovercoming the force of said spring and urging said valve member to saidactuated position; and wherein said control means include a bypassconduit means connecting the inlet and outlet of said main pump andhaving ports on said valve casing, and a duct means formed in said valvemember and connecting said ports in said actuated position of said valvemember so that fluid is pumped by said main pump through said bypassconduit and said duct means and discharge through said consumer conduitis terminated.

1 l. Arrangement as claimed in claim 10 wherein said control meansinclude a check valve in said feed conduit downstream of said filtermeans and upstream of said bypass conduit for protecting said filtermeans.

12. Arrangement as claimed in claim 1 wherein said control means includehydraulic regulating means for said main pump; wherein said pressureresponsive means include a pressure responsive valve responsive to saidpredetermined pressure differential to move out of said normalinoperative position to said actuated position, and connecting in saidactuated position said feed conduit with said hydraulic regulating meansto operate the latter to set said main pump to pump a reduced amount offluid; wherein said pressure responsive valve in said normal inoperativeposition connects said feed conduit with a discharge outlet; and whereinsaid pressure responsive valve includes a spring urging the same to saidnormal inoperative position.

13. Arrangement as claimed in claim 12 wherein said regulating meansinclude a cylinder, and a differential piston and piston rod in saidcylinder forming in the same a piston chamber and a piston rod chamber;wherein said piston chamber is connected with said feed conduit in saidactuated position of said pressure responsive valve, and with saiddischarge outlet in said normal inoperative position; and wherein saidpiston rod chamber is connected with said consumer conduit.

14. Arrangement as claimed in claim 13 wherein said regulating meansinclude manually operated means for moving said piston and piston rod insaid cylinder to a position in which said regulating means set said mainpump to maximum output which is reduced by said regulating means whensaid predetermined pressure differential prevails at said filter meansand fluid from said consumer conduit flows into said piston rod chamberwhile said piston chamber is connected with said discharge outlet.

15. Arrangement as claimed in claim 12 comprising a pressure limitingvalve connected with said feed conduit between said feed pump and saidfilter means and having a discharge outlet for discharging fluid fromsaid feed conduit when the pressure in the same exceeds a normalpressure.

16. Arrangement as claimed in claim I wherein said main pump has aconstant output volume; and wherein said control means include a conduitconnecting the inlet and outlet of said main pump, and a control valvein said conduit having a position connecting said inlet with said outletfor idle circulation.

l7. Arrangement as claimed in claim 1 wherein said control means includeregulating means for said main pump; and wherein said pressureresponsive means in said actuated position operate said regulating meansto reduce the output volume of said main pump.

18. Arrangement as claimed in claim 1 wherein said pressure responsivemeans include a valve having a discharge outlet closed in said normalinoperative position, and connecting said feed conduit upstream of saidfilter means with said discharge outlet in said actuated position sothat the flow through said filter is reduced when said predeterminedpressure differential indicates a faulty condition of said filter means.

1. Arrangement for pumping a filtered fluid, comprising a feed pump;main pump means including a main pump, and a consumer conduit throughwhich said main pump discharges; feed conduit means connecting said feedpump with said main pump so that only fluid pumped by said feed pumpinto said feed conduit means flows into said main pump; filter means insaid feed conduit means having a working condition causing a normalpressure differential in said feed conduit means, said filter meansbeing disposed across the flow cross section of said feed conduit meansso that all the fluid flowing in said feed conduit means to said mainpump means flows through said filter means, and no fluid in unfilteredcondition bypasses said filter means and flows into said main pump;pressure responsive means connected with said feed conduit meansupstream and downstream of said filter means and being in a normalinoperative position when said normal pressure differential indicatessaid working condition of said filter means, said pressure responsivemeans moving to an actuated position in response to a predeterminedpressure differential different from said normal pressure differentialand indicating a faulty filtering action of said filter means; andcontrol means for said main pump means operated by said pressureresponsive means in said actuated position to terminate discharge fromsaid main pump into said consumer conduit.
 2. Arrangement as claimed incLaim 1 wherein said main pump discharges a constant amount of fluid;wherein said control means include a control valve means having anoperative position connecting said main pump with said consumer conduit,and a control position in which said main pump idles; and wherein saidpressure responsive means include a pressure responsive valve respondingto said predetermined pressure differential to move to said actuatedposition, and connecting in said actuated position said feed conduitbetween said feed pump and said filter means with said control valvemeans for moving the same from said normal position to said controlposition.
 3. Arrangement as claimed in claim 1 wherein said controlmeans include hydraulic regulating means for said main pump; and whereinsaid pressure responsive means include a pressure responsive valveresponding to said predetermined pressure differential to move to saidactuated position, and connecting in said actuated position said feedconduit between said feed pump and said filter means with said hydraulicregulating means so that fluid flowing from said feed pump to saidhydraulic regulating means operates the latter to set said main pump topump a minimum amount of fluid.
 4. Arrangement as claimed in claim 1wherein said pressure responsive means include a pressure responsivevalve including a movable valve member, and a spring biassing said valvemember into said normal inoperative position; wherein said control meansinclude a control conduit; wherein said valve in said actuated positionconnects said feed conduit and said control conduit, respectively;wherein said predetermined pressure differential overcomes the force ofsaid spring and moves said valve member to said actuated position; andwherein said control means are hydraulic control means operated in saidactuated position of said valve by fluid flowing from said feed pumpthrough said valve and said control conduit.
 5. Arrangement as claimedin claim 1 comprising a discharge conduit connected with said feedconduit downstream of said filter means; and a pressure limiting valvein said discharge conduit spring biassed to a first position closingsaid discharge conduit when the pressure in said feed conduit is low,and at least a second position for supplying fluid to said control meansfor holding the same in a normal position in which said main pumpdischarges through said consumer conduit fluid fed by said feed pump ata normal pressure.
 6. Arrangement as claimed in claim 1 wherein saidcontrol means include a control valve means including a control valvemember, a valve casing, and a spring biassing said control valve memberto a first position closing said consumer conduit; comprising a returnconduit connecting said valve casing with said feed conduit downstreamof said filter means and being connected with said consumer conduit insaid first position so that said main pump idles, said control valvemember having a second working position closing said return conduit andopening said consumer conduit; first and second control conduitsconnected with said valve casing so that pressure in said first controlconduit acts on said control valve member to move the same to said firstposition, and pressure in said second conduit acts on said control valvemember to move to said second working position; wherein said pressureresponsive means include a pressure responsive valve connecting in saidactuated position said feed conduit between said feed pump and saidfilter means with said first control conduit so that at saidpredetermined pressure differential said control valve member closessaid consumer conduit; and comprising a pressure limiting valveconnected with said feed conduit downstream of said filter means andincluding a limit spring urging said pressure limiting valve to a closedposition, said pressure limiting valve moving to an operative positionconnecting said feed conduit with said second control conduit when thepressure in said feed conduit overcomes the force of Said limit springso that said control valve member is moved to said second workingposition.
 7. Arrangement as claimed in claim 6 wherein said pressurelimiting valve in said closed and operative positions disconnects saidfeed conduit from a discharge outlet, and has a third position assumedat high pressure in said feed conduit for connecting said feed conduitwith said discharge outlet and with said second control conduit. 8.Arrangement as claimed in claim 1 wherein said control means includehydraulic regulating means for said main pump; wherein said pressureresponsive means include a pressure responsive valve responding to saidpredetermined pressure differential to move to said actuated position,and connecting in said actuated position said feed conduit between saidfeed pump and said filter means with said hydraulic regulating means sothat fluid flowing from said feed pump to said hydraulic regulatingmeans operates the latter to set said main pump to pump a minimum amountof fluid; and wherein said regulating means further include manuallyoperated means, and hydraulic arresting means for arresting saidmanually operated means.
 9. Arrangement as claimed in claim 8 comprisinga pressure limiting valve connected with said feed conduit; wherein saidhydraulic arresting means include a cylinder, and a piston forming insaid cylinder first and second chambers; said first chamber beingconnected by said pressure responsive valve with said feed conduitupstream of said filter means, and said second chamber being connectedby said pressure limiting valve with said feed conduit downstream ofsaid filter means; and wherein said hydraulic arresting means furtherinclude an arresting member operated by said piston so that saidmanually operated means are arrested when high pressure fluid from saidfeed conduit is supplied to said first chamber, and are released by highpressure fluid supplied to said second chamber.
 10. Arrangement asclaimed in claim 1 wherein said pressure responsive means include avalve casing, two conduits connecting said valve casuing with said feedconduit upstream and downstream of said filter means, a valve member insaid casing between said conduits so that the pressure differentialcaused by said filter means acts on said valve member, and a springacting on said valve member and urging the same into said normalinoperative position, said predetermined pressure differentialovercoming the force of said spring and urging said valve member to saidactuated position; and wherein said control means include a bypassconduit means connecting the inlet and outlet of said main pump andhaving ports on said valve casing, and a duct means formed in said valvemember and connecting said ports in said actuated position of said valvemember so that fluid is pumped by said main pump through said bypassconduit and said duct means and discharge through said consumer conduitis terminated.
 11. Arrangement as claimed in claim 10 wherein saidcontrol means include a check valve in said feed conduit downstream ofsaid filter means and upstream of said bypass conduit for protectingsaid filter means.
 12. Arrangement as claimed in claim 1 wherein saidcontrol means include hydraulic regulating means for said main pump;wherein said pressure responsive means include a pressure responsivevalve responsive to said predetermined pressure differential to move outof said normal inoperative position to said actuated position, andconnecting in said actuated position said feed conduit with saidhydraulic regulating means to operate the latter to set said main pumpto pump a reduced amount of fluid; wherein said pressure responsivevalve in said normal inoperative position connects said feed conduitwith a discharge outlet; and wherein said pressure responsive valveincludes a spring urging the same to said normal inoperative position.13. Arrangement as claimed in claim 12 wherein said regulating meansinclude a cylinder, and a differential pistoN and piston rod in saidcylinder forming in the same a piston chamber and a piston rod chamber;wherein said piston chamber is connected with said feed conduit in saidactuated position of said pressure responsive valve, and with saiddischarge outlet in said normal inoperative position; and wherein saidpiston rod chamber is connected with said consumer conduit. 14.Arrangement as claimed in claim 13 wherein said regulating means includemanually operated means for moving said piston and piston rod in saidcylinder to a position in which said regulating means set said main pumpto maximum output which is reduced by said regulating means when saidpredetermined pressure differential prevails at said filter means andfluid from said consumer conduit flows into said piston rod chamberwhile said piston chamber is connected with said discharge outlet. 15.Arrangement as claimed in claim 12 comprising a pressure limiting valveconnected with said feed conduit between said feed pump and said filtermeans and having a discharge outlet for discharging fluid from said feedconduit when the pressure in the same exceeds a normal pressure. 16.Arrangement as claimed in claim 1 wherein said main pump has a constantoutput volume; and wherein said control means include a conduitconnecting the inlet and outlet of said main pump, and a control valvein said conduit having a position connecting said inlet with said outletfor idle circulation.
 17. Arrangement as claimed in claim 1 wherein saidcontrol means include regulating means for said main pump; and whereinsaid pressure responsive means in said actuated position operate saidregulating means to reduce the output volume of said main pump. 18.Arrangement as claimed in claim 1 wherein said pressure responsive meansinclude a valve having a discharge outlet closed in said normalinoperative position, and connecting said feed conduit upstream of saidfilter means with said discharge outlet in said actuated position sothat the flow through said filter is reduced when said predeterminedpressure differential indicates a faulty condition of said filter means.